Continuous plating system and method with mask registration

ABSTRACT

A continuous plating system with mask registration is disclosed herein that uses drums and rollers with protruding pins which engage with guide holes in a masking belt and a lead frame. Through engagement with the pins the masking belt is keyed to the lead frame as the lead frame passes through a plating solution tank.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.11/278,947 filed Apr. 6, 2006, which claims priority from provisionalapplication Ser. No. 60/669,070 filed Apr. 6, 2005, and is acontinuation-in-part of non-provisional application Ser. No. 11/388,245filed Mar. 23, 2006.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is generally related to plating systems, and morein particular, continuous plating systems.

2. Description of the Related Art

Conventional approaches for plating metals onto portions of targetedparts can involve either a generally more precise step-and-repeatplating for plating selective locations or a generally faster continuousstrip plating for plating portions of parts whose intended plating areascan be arranged in an uninterrupted path. Such targeted parts can befound joined together in a lead frame. A lead frame can be formed as along continuous strip containing duplicate copies of a particular part.The lead frame can be fed through machines to perform various physicalmanipulations on each of the parts of the lead frame in an orderlystepwise fashion so that each of the parts has its turn to undergo eachof the physical manipulations performed by the machines.

With the conventional step-and-repeat plating process, a precise mask offinite length is positioned over a section of a lead frame having aseries of parts. The mask has various openings so that for each part ofthe masked lead frame section, those portions of the part that are to beplated remains unmasked. The unmasked portions of the parts of themasked lead frame section are subsequently exposed to a plating solutionto accomplish their plating.

The lead frame is typically negatively charged to plate those exposedareas of the lead frame when they receive plating solution such as bypouring, spraying, or brushing the solution from a positively chargedapplicator, such as a nozzle. After the unmasked portions of the partsof the masked lead frame section have been plated, a new section of thelead frame is moved to be masked and to further repeat thestep-and-repeat process.

Some implementations of the step-and-repeat process involve perforatedtape masks that are each used for a portion of the lead frame and aresubsequently removed and discarded after plating of the respectiveportion of the lead frame is accomplished. Although the step-and-repeatprocess can be used for precision plating so that relatively littleplating material is wasted, the process can be inherently slow and laborintensive.

With a conventional continuous plating system, the lead frames can berun at constant velocity through the plating system thereforepotentially reducing labor requirements and potentially increasingthroughput. Conventional continuous plating systems include a de-reeler,welding apparatus, tanks, guide devices, masking belt and a re-reeler.The de-reeler feeds the lead frame from a first reel into the platingsystem. The welding apparatus includes a spot welder and a weldingfixture to attach subsequent reels of lead frames to be fed into theplating system.

The tanks includes a series of cleaning, plating and washing tanks toelectroplate nickel, gold or other precious metals on to portions of theparts of the lead frame. The guide devices are fashioned to direct thelead frame through the tanks while trapping the parts between the movingmasking belts. The masking belt exposes one or more portions of eachpart of the lead frame through one or more openings in the masking beltto plating solution to be plated and covers other portions of each partto prevent those portions from being plated.

The re-reeler spools the plated parts onto a second reel as the partsemerge from the plating system. Within reason, the longer the portion ofthe lead frame that can be exposed to the plating solution at any onetime, the faster the lead frame can be run through the continuousplating system and consequently, the faster the throughput of thecontinuous plating system.

Although conventional continuous plating systems can have relativelyfaster throughput than the conventional step-and-repeat plating systems,there is a price for this faster throughput with conventional continuousplating systems. Namely, conventional continuous plating systems tend tobe more wasteful of the plating materials.

A problem exists with conventional continuous plating systems in thatthe masking belt typically shifts back and forth in position orthogonalto its direction of motion, also referred to as trans-linear motion.This trans-linear motion causes a shift back and forth in position ofeach of the openings in the masking belt relative to its associated leadframe part to be masked. The trans-linear back and forth shifting ofposition of the opening thus creates uncertainty as to where the openingwill be positioned with respect to the particular lead frame part at thepoint when plating of the part occurs.

Consequently, if the opening was only as large as its correspondingdesired portion of the part to receive plating, this desired portion ofthe part may not be fully plated. Through the trans-linear shifting, theopening may not be properly positioned over the part at the time ofplating. Rather, the opening may be somewhat out of position and if theopening was only the size of the desired portion of the part to beplated, not all of the desired portion of the part would be exposedthrough the opening to receive the plating solution.

Thus, to compensate for this shifting due to the trans-linear motion,each of the openings are enlarged enough so that no matter where anopening is in its back and forth trans-linear motion, all of the desiredportion of the part to be plated is still exposed through the opening toreceive the plating solution. This compensation, however, has a price.Since the opening in the masking belt is larger than the desired portionof the part to be plated, areas of the part that do not require platingwill be resident in the area of the opening and will be plated, whichwastes the plating metal.

This enlargement of the opening larger than the desired portion of thepart to be plated is referred to as over-plating. With some conventionalimplementations of continuous plating systems an over-plating of 0.06inches on either side of the desired portion of the part to be plated isnot an unusual value.

Some conventional implementations of the continuous plating system maytry to use masking belts of relatively greater thickness to possiblyreduce the amount of trans-linear motion. A drawback of increasedmasking belt thickness is a result referred to as a wall effect in whichthe mask thickness inhibits the thickness of the plating near the edgeof the opening. The combination of an opening of the belt mask with oneof the lead frame parts forms a sort of canyon with the part acting assort of the floor of the canyon and the edges of the opening actingsomewhat like vertical walls of the canyon.

As the lead frame part is pressed with the mask belt and is movedthrough the tank of plating solution, the plating solution enters the socalled canyon, but interaction of the plating solution with the walls ofthe canyon somewhat hinders the plating solution from depositing platingmaterial to as great an extent on the floor of the canyon (a portion ofa part of the lead frame) near the walls of the canyon (edges of theopening) when compared to the amount of plating material depositedfarther away from the walls.

As a result, the plating material on a plated portion of a part has anuneven thickness, being thinner near the edges of the plated portion andbeing thicker near the center of the plated portion. Generally speaking,the thicker the belt mask, the larger the difference in thickness isbetween the edges and the center of a given plated portion. Resultantuneven plating can also waste plating material because more platingmaterial may need to be used in a center of a plated portion in order tohave a sufficient amount of plating material near the edges of theplated portion.

The cost of plating precious metals is primarily determined by theamount of gold or other precious metal used and the throughput speedinvolved. The two conventional approaches discussed raise costs byeither being relatively slow and labor intensive, or by being relativelywasteful of plating material.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 is an isometric view of a continuous plating system with maskregistration.

FIG. 2 is a cross-sectional view of the plating system takensubstantially along the line 2-2 of FIG. 1.

FIG. 3 is an enlarged, cross-sectional view of a portion of the platingsystem of FIG. 1.

FIG. 4 is an enlarged fragmentary view of the masking belt of theplating system.

FIG. 5 is an enlarged section view of the masking belt coupling with thelead frame of the plating system.

FIG. 6 is a cross-sectional view of the plating system takensubstantially along the line 6-6 of FIG. 3.

FIG. 7 is a cross-sectional view of the plating system takensubstantially along the line of 7-7 FIG. 3.

FIG. 8 is an enlarged, isometric view of a representative pin profile.

FIG. 9 is a side elevational view of the pin profile of FIG. 8.

FIG. 10 is an isometric view of an alternative lead frame configured forstrip plating.

FIG. 11 is an isometric view of an alternative continuous plating systemwith mask registration for strip plating.

FIG. 12 is an enlarged, cross-sectional view of a portion of thealternative plating system substantially along the line 12-12 of FIG.11.

FIG. 13 is an enlarged fragmentary view of the alternative masking beltof the alternative plating system.

FIG. 14 is an enlarged section view of the alternative masking beltcoupling with the alternative lead frame of the alternative platingsystem.

FIG. 15 is a cross-sectional view of the alternative plating systemtaken substantially along the line 16-16 of FIG. 33.

FIG. 16 is a cross-sectional view of the alternative plating systemhaving an alternative drive wheel.

DETAILED DESCRIPTION OF THE INVENTION

A continuous plating system with mask registration is disclosed hereinthat uses drums and rollers with protruding pins which engage with guideholes in a masking belt and a lead frame. Through engagement with thepins the masking belt is keyed to the lead frame as the lead framepasses through a plating solution tank. The continuous plating systemcan be used to maintain precise registry both in the direction of parttravel and perpendicular to travel of the parts to be plated for spotplating. The masking belt has openings that remain in registeredpositions relative to associated parts on the lead frame so that littleif any trans-linear motion occurs and so that part areas to be platedare exposed to plating solution accurately and consistently. This cangreatly reduce the amount of over-plating present.

Furthermore, in some implementations, due in part to the relative lackof trans-linear motion through registration of the masking belt with thelead frame, the thickness of the masking belt can be reduced. Thisreduction in thickness of the masking belt can result in a reduction ofpotential wall effects resulting in more consistent plating thickness.As a consequence, the amount of plating material used for a givenapplication can be reduced.

As will be described in greater detail, the continuous plating systemwith mask registration teaches in general, systems and methods thatselectively electroplate a strip of material, such as a lead frame, incontinuous fashion. At one stage of travel, the strip engages with pinsof a relatively large externally drive wheel, is looped partially aroundthe drive wheel, and is consequently pulled through an open top platingtank of electrolyte solution. Before the strip is sent through the tank,a loop of perforated masking material, otherwise referred to herein as amasking belt, also engages with the pins of the drive wheel to beregistered in step with the strip so as to precisely expose only theareas on the strip which require plating as the strip passes through thetank.

In an exemplary implementation, the drive wheel has its periphery sizedin circumference to accommodate pins all substantially equally spacedaround the circumference of the drive wheel. The pitch spacing of thepins around the first drum circumference and around the wheelcircumference is matched to the pitch spacing of guide holes in thestrip so that in these implementations, the circumference of the firstdrum, the circumference of the drive wheel, and any other circumferencehaving pins is divisible by the pitch spacing of the pins. Materialselection for the drive wheel and masking belt also considers thermalexpansion due to operating temperatures of the plating solution.

For instances in which the strip is a lead frame, a lead frame typicallyrequires such guide holes for a hitch feed mechanism used in theprogressive dies that stamp and form the parts of the lead frame. Themasking belt is punched with holes at the same pitch spacing as guideholes on the strip and pins on the drive wheel for registry with thestrip. The masking belt is also punched with openings to match areas onthe strip requiring the selective plating. In construction of themasking belt, a fixture with punch and die is used for adjustable andaccurate pitch spacing of masking belt guide holes. Care is also usedwhen splicing the masking belt material together to form the maskingbelt to insure that pitch spacing of the guide holes is maintained.

A spring loaded compliance arm can be used to trap the strip between thedrive wheel and the masking belt. Additionally, tracking rollers alsoequipped with pins are used in the return path of the masking belt tobetter insure stable tracking of the belt. The tracking rollers alsopermit use of a thin masking belt design to reduce wall effects. Beforeand after engagement with the drive wheel, the strip is drawn overrotating negatively charged first and second drums, respectively, whichprovide the cathode of the process.

A band concentric and in close proximity to the periphery of the portionof the drive wheel in the plating solution provides the anode of thecircuit. The band is fluted to allow plating solution to be continuouslypumped through the flutes to be in proximity to the masked portions ofthe strip. This fluid motion and rapid exchange accelerates andmaintains the consistency of the plating process.

As shown in FIG. 1, a continuous plating system 100 sequentiallyreceives a strip, such as a lead frame 102, having a first side 102 aand a second side 102 b and having duplicate copies of a part 104serially arranged along the lead frame, each of the parts to be platedon one or more portions of the second side. Serial portions of the leadframe 102 are sequentially moved in a continuous manner by the system100 into a tank 106 of plating solution 108 and sequentially emerge fromthe tank with a portion of the second side 102 b being plated. The parts104 are sequentially plated on the second side 102 b on portions of theparts exposed to the plating solution 108 through serially arrangedopenings 112 of a masking belt 114. The masking belt 114 is made from alow profile rubber covered polyamide core material, such as rapplon,which survives associated environmental and mechanical abuse, performsas an effective mask, and minimizes wall effect by its low profile.

In the depicted implementation, there is one of the openings 112 foreach of the parts 104, but in other implementations there can be morethan one of the openings for each of the parts. Serial portions of thelead frame 102 are sequentially received by a first cathode drum 116 ofthe system 100 around whose circumference the lead frame is partiallywrapped to be directed downward in a continuous manner toward theplating solution 108. The first cathode drum 116 imparts a negativecharge to the serial portions of the lead frame 102 through conductiveproperties of the lead frame to attract positively charged metalconstituents of the plating solution 108. Upon sequentially leaving thefirst cathode drum 116, serial portions of the lead frame 102 join withserial portions of the masking belt 114 to be sequentially wrappedaround the partial circumference of an electrically non-conductivecarrier or drive wheel 118 which is rotatable about its axis. In someimplementations, material used for the drive wheel 118 is an acrylicplastic, which also has predictable thermal expansion properties.

The drive wheel 118 sequentially guides the serial portions of the leadframe 102 and the masking belt 114 through the plating solution 108.After plating is sequentially accomplished, serial portions of the leadframe 102 and the masking belt 114 sequentially emerge from the platingsolution 108 and they separate from one another. Serial portions of thelead frame 102 then sequentially wrap partially around a second cathodedrum 120, which imparts a negative charge to the lead frame, and thensequentially exit the system 100.

As serial portions of the lead frame 102 and serial portions of themasking belt 114 sequentially pass through the plating solution 108,they sequentially pass by a fluted anode member or band 122 better shownin FIGS. 2 and 3. The fluted anode band 122 has a profile inverse to aportion of the circumference of the drive wheel 118 and extends along aportion of the periphery of the drive wheel in close proximity to thedrive wheel. The band 122 imparts a positive charge to constituents ofthe plating solution 108 as the plating solution passes through flutesof the band as described further below.

The masking belt 114 has substantially equally spaced guide holes 124,better shown in FIG. 4, and the lead frame 102 has substantially equallyspaced guide holes 126, better shown in FIG. 5. The guide holes 124 ofthe masking belt 114 and the guide holes 126 of the lead frame 102 havesubstantially the same spacing. As serial portions of the lead frame 102and serial portions of the masking belt 114 sequentially approach thedrive wheel 118 each of the guide holes 124 of the masking belt alignwith a different one of the guide holes 126 of the lead frame 102, asshown in FIG. 5, to receive a pin 128 of the drive wheel, as shown inFIGS. 6 and 7. As shown in FIG. 7, in the depicted embodiment, the pins128 are held in position by side tap screws 129 countersunk into thedrive wheel 118. After plating as the serial portions of the lead frame102 and the masking belt 114 sequentially separate from each other, theguide holes 124 of the masking belt and the guide holes of the leadframe disengage from the pins 128 of the drive wheel 118, as shown inFIG. 3.

Tracking rollers 130, shown in FIGS. 1 and 2, with pins 132 arepositioned along the path of the masking belt 114 to keep the maskingbelt in proper alignment at the point where serial portions of themasking belt sequentially join with serial portions of the lead frame102. The pins 132 are substantially equally spaced along thecircumference of the tracking rollers 130 and are spaced from oneanother the same distance as found with the guide holes 124 of themasking belt 114. As serial portions of the masking belt 114sequentially pass by one of the tracking rollers 130, the guide holes124 of the masking belt engage with the pins 132 of the tracking roller.Thus, the tracking rollers 130 help to prevent or lessen the amount oftrans-linear motion of the masking belt 114.

Belt pulleys 134 are positioned along the path of the masking belt 114to dampen tension variations and vibration induced in the masking beltby applying force to the masking belt as the masking belt moves alongits path. The belt pulleys 134 otherwise help guide the masking beltwhile leaving reduction of trans-linear motion of the masking belt to bemainly addressed by the drive wheel 118 and the tracking rollers 130. Inthe depicted implementation, only the drive wheel 118 is driven by amotive member such as a motor although other implementations can haveother drive arrangements. A sealing belt 136 extends around a majorportion of the circumference of the drive wheel 118 and partially aroundan idler pulley 140. The sealing belt 136 is axially mid-positioned onthe drive wheel 118 to be in sequential alignment with serial portionsof the lead frame 102 by riding in a belt groove 138 located around thecircumference of the drive wheel 118, as shown in FIG. 1. The sealingbelt 136 serves to seal the first side 102 a of serial portions of thelead frame 102 from plating solution 108 as they sequentially travelthrough the tank 106.

To help maintain a seal between the first side 102 a of serial portionsof the lead frame 102 and serial portions of the sealing belt 136, andalso a seal between serial portions of the masking belt 114 and serialportions of the second side 102 b of the lead frame 102, a spring loadedcompliance arm 141, shown in FIG. 2, is positioned to press againstserial portions of the masking belt and the lead frame near the point atwhich they sequentially engage with the pins 128 of the drive wheel 118.

For the lead frame 102 depicted in FIG. 5, a set of four tines 142 ofeach of the parts 104 are plated. As shown in FIG. 6, each of the setsof tines 142 is exposed to the plating solution 108 through one of theopenings 112. The set of tines 142 passes by the fluted anode band 122through which the plating solution 108 passes through a plurality offlutes 144, as shown in FIG. 7, to be directed near and onto the secondside 102 b of the set of tines 142.

The pins 128 of the drive wheel 118 have a profile that allows smoothentry and release of the lead frame 102 and the masking belt 114. Thepins 132 of the tracking rollers 130 have a profile that allows smoothentry and release of the masking belt 114. A representative pin profile146 for the pins 128 and the pins 132 is shown in FIGS. 8 and 9 ashaving a tapered end portion 148 that guides entry and release of thelead frame 102 and/or masking belt 114.

A curved section 150 provides adjustment for the lead frame 102 and/ormasking belt 114 to transition from the tapered end portion 148 to acylindrical portion 152 with relatively larger diameter to temporarilyretain the lead frame 102 and/or masking belt 114 to maintain alignment.Material selection for the pins 128 of the drive wheel 118 generally areelectrically non-conductive for practical orders of magnitude. Materialselection for the pins 128 of the drive wheel 118 and the pins 132 ofthe tracking rollers 130 have high abrasion resistance and high tensilestrength. For instance, ceramic materials can be used for the pins 128of the drive wheel 118 and stainless steel materials can be used forpins 132 of the tracking rollers 130. A recessed portion 154 receivesthe side screw 129 to retain the pins 128 in the drive wheel 118 and thepins 132 in the tracking rollers 130.

An alternative strip version of the lead frame 102 is shown in FIG. 10having the portions of the tines 142 to be plated exclusively orientedwithin two illustrative boundary lines, B, running parallel with thelongitudinal dimension, Z, of the lead frame. Since the only portions ofthe lead frame 102 within the two boundary lines, B, are to be plated onthe second side 102 b, an alternative version of the masking belt 114can be used that need only be precisely registered with the lead frameregarding the transverse dimension, Y, of the lead frame.

Consequently, an alternative continuous plating system 200, shown inFIG. 11 and FIG. 12, generally has most of the components of thecontinuous plating system 100, however, the masking belt 114 has a stripopening 202 running longitudinally along the masking belt so that themasking belt is actually two belts 114 a and 114 b transversely spacedby the width of the strip opening. In turn, the width of the stripopening 202, better shown in FIG. 13 and FIG. 14, is the distance in thetransverse dimension, Y, between the two boundary lines, B, so that onlythat the portion of the second side 102 b of the tines 142 that needs toplated is exposed to the plating solution 108. The drive wheel 118 forthe alternative continuous plating system 200, better shown in FIG. 15,includes a lead frame groove 204 with beveled sides 206 to receive thelead frame 102 and prevent excessive transverse motion of the lead framewithout requiring the guide holes 126 of the lead frame 102 to bereceived by the pins 128 of the drive wheel.

A second implementation of the drive wheel 118, shown in FIG. 16 for thealternative continuous plating system 200 has two outer sections 118 aand an inner section 118 b. The two outer sections 118 a and the innersection 118 b can be uncoupled from one another to exchange differentversions of the inner section 118 b that may have different sizing ortransverse positioning of the lead frame groove 204 and/or the beltgroove 138 as exemplified by differences in positioning shown in FIG. 15and FIG. 16.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

1. A method for plating a portion of each of a plurality of seriallyarranged parts of a lead frame with plating solution, the lead framehaving a plurality of guide holes, a method comprising: providing a tankcontaining a plating solution; providing a masking belt having alongitudinally extending opening and a plurality of guide holes;providing a drive wheel having a plurality of pins; providing aplurality of tracking rollers each having a plurality of pins;sequentially engaging the plurality of pins of the drive wheel with theplurality of guide holes of the masking belt and sequentially engaging agroove of the drive wheel with portions of the lead frame tosequentially register each of the plurality of serially arrangedopenings of the masking belt with the portion of different parts of thelead frame; sequentially passing the serially arranged parts through thetank of plating solution; and sequentially engaging the plurality ofpins of each of the plurality of tracking rollers with the plurality ofguide holes of the masking belt to assist in maintaining alignment ofthe masking belt and the registering of the openings with the parts. 2.A method for plating a portion of each of a plurality of seriallyarranged parts of a lead frame with a plating solution, the lead framehaving a plurality of guide holes, the method comprising: providing amasking belt with a width and a length, the belt having an openingextending a distance along the length greater than the width openingsand a plurality of guide holes; providing a drive wheel having aplurality of pins and a peripheral groove; and engaging the groove ofthe drive wheel with the lead frame and the plurality of pins with theplurality of guide holes of the masking belt to sequentially registerthe opening of the masking belt with the portion of different parts ofthe lead frame, whereby the opening of the masking belt is aligned withthe portion of different parts of the lead frame to expose the portionto the plating solution.
 3. A method for plating a portion of each of aplurality of serially arranged parts of a lead frame with a platingsolution, the lead frame having a plurality of guide holes, the methodcomprising: providing a masking belt having a plurality of guide holes;providing a tracking roller having a plurality of pins; and engaging theplurality of pins of the tracking roller with the plurality of guideholes of the masking belt to assist in maintaining alignment of serialportions of the masking belt with serial portions of the lead frame.